IMO that is not how I would describe his better choral works (he does get a bit repetetive in the less-significant ones such as the mass, though). I find him absolutely gripping when at his best. The Stabat Mater is mandatory IMO, probably his greatest composition, the Passion is also remarkable although the length tests many peoples patience.
Tabula Rasa is another that needs to be heard, again, the second movement could test ones patience, but the first movement shows him at his best and the contrast between the movements is startling.
Edit: One feature of some of his early instrumental writing in his "mature" style (eg Tabula Rasa, Summa, Cantus, Fratres, Festina Lente) is just how confident they sound - written at a time when serialism was popular, this is blatently melodic, semi-minimal and atmospheric music written masterfully.
I would also add Fur Alina and Spiegel im Spiegel (on the ECM disc if possible) to the "must hear" list.
Bingo! I agree with every word, every recommendation! This is the hard core of Part's tintinabuli pieces - I'd add only
Es sang vor langen Jahren, which is possibly, along with the Stabat Mater, my favourite Part piece. After these pieces Part began to dilute the style somewhat, to equally diluted effect IMO. Although I'd include the
Miserere amongst those diluted pieces (though not so much as others such as
Litany) I'd also say that it is one of Part's most powerful pieces and I recommend it wholeheartedly too. I've talked about this before, about the unusual situation Part must have found himself in. Here he was, having discovered/created/whatever this
perfect style and technique - I use the word advisedly because, like it or not, the tintinabulism technique is absolutely flawless from every angle, on its own terms. What could he do now - repeat himself? I don't think so, for all sorts of reasons. Or try to develop the technique? Well, that's what he did, adding variations and extensions to the technique which, whilst it broadened its scope, lessened its impact. That's why, to restate my first point, that small list of pieces:
Stabat Mater
Passio
Fratres
Tabula Rasa
Festina Lente
Spiegel im spiegel
Es sang vor langen Jahrenwill IMO stay the central, perfect focus of his output. And we can hardly complain!
Is Tabula Rasa the work that includes the two movements: Ludus and Silentium? And I guess you're praising "Ludus", which infact really moved me at first listening, though now I'm unable to enjoy it with the same interest. Silentium, instead, is a sort of static snapshot of great impact and sound, but that's it in my opinion.
For what concerns Spiegel in Spiegel for violin and piano, no I cannot honestly enjoy something like hearing two piano pupils working on rhythm subdivision for 10 minutes 
I think, with both these pieces, if you were to quietly concentrate on the process in each piece - spell-binding and utterly logical - you might overcome your problem; listening to them as one listens to other 'pretty' tonal music may well lead to exasperation. They call for a kind of attentive meditation, I think. The power of Part's tintinabulism to create these beautiful but completely process-driven pieces is really quite incredible, and the reason I call it perfect. In
Spiegel im spiegel the process is at its most bare and fragile, and it's very beautiful and moving to follow the way the line expands note by note, I think. In Tabula Rasa, simply because of the larger forces and more diverse material, it is somewhat more complex, but very clear once understood. The best example I have of the overwhelming logic of the technique is anecdotal; indulge me:
When I was about 15 I began to collect the ECM Part LPs avidly, and an early purchase was the Passio disc. This work starts with a choral exhortation, before settling down for about 70 minutes of the Passion itself; at the
very end, though, with Jesus' words 'consumatum est', the music changes course somewhat, and then concludes with another sequence of choral writing.
Well, remarkably, even though I was hearing the piece for the first time, I was able, follwoing the words, to tell
before it happened exactly what Part would do in that last minute or so of music; indeed, I sang along with the music!
Much later - last year, actually - I got hold of Paul Hillier's wonderful book on Part and was astonished - or maybe not - to find that, indeed, although the end of Passio is so different from what comes before, it is at the same time implicit in all that has gone before. The fact that I 'predicted it' was then, I suppose, less surprising. Incidentally, I consider this clear evidence of the power of analysis to explain responses to music; in this case it told me, 15 years after the even, precisely why my peculiar response to the piece had occured.
